Resistance welding of railroad rails is often used to join two rail sections together as a rail way is built or repaired. This type of welding is commonly referred to as “flash butt” welding. Flash butt welding is distinguished from conventional pot welding where a filler material is flowed into the weld joint.
Pot welding, which is based on adding filler material to a metal joint, can be viewed as a form of casting. During a pot weld, liquid metal is used as a filler material. As the filler material later transforms from liquid to solid metal during cooling of the weld, the filler material, which is typically steel, shrinks several percent, drawing material from the risers on either side of the base and from above the head. Voids from this shrinkage, as well as sand inclusions from the mold and oxide inclusions from splashing, tend to reduce the strength and life of the weld.
These problems are largely solved by flash butt welding. During flash butt welding, the two rails ends to be joined are first heated and then forged together, expelling liquid and oxides from the weld joint. The forged joint is sheared to remove the flash, which is solidified material that was forced out of the joint during forging.
As noted above, a typical flash butt weld requires two operations: (1) closing a gap in the track, and (2) heating the joint to forge the rail ends. Existing in-track weld heads have insufficient power and stroke length to execute large gap/large force closures without employing additional equipment in conjunction with the head. In particular, for example, the execution of a closure weld when a large amount of force is required to pull the rails together is performed with a separate pull assistance device working in conjunction with the welding head. During this type of operation, the pull force, timing and alignment of each device has to be coordinated in a complex and time consuming manner that requires extensive operator skill and oversight.
When considering this background section, the disclosure and claims herein should not be limited by the deficiencies of the prior art. In other words, the solution of those deficiencies is not a critical limitation of any claim unless otherwise expressly noted in that claim. Moreover, while this background section is presented as a convenience to the reader who may not be of skill in this art, it will be appreciated that this section is too brief to attempt to accurately and completely survey the prior art. The preceding background description is thus a simplified and anecdotal narrative and is not intended to replace printed references in the art. To the extent an inconsistency or omission between the demonstrated state of the printed art and the foregoing narrative exists, the foregoing narrative is not intended to cure such inconsistency or omission. Rather, applicants would defer to the demonstrated state of the printed art.